1. Field of the Invention
This invention relates to printed circuit boards, and more particularly to use of optical fibers in printed circuit boards for communication.
2. Background of the Invention
A printed circuit board (“PCB”) is a structure to which electronic devices are attached. The PCB has one or more structural layers as well as patterned conductors. The structural layers support the electronic devices while the conductors provide power to the electronic devices and allow devices to communicate through use of electronic signals.
FIG. 1 is a cross-sectional side view of a portion of a typical conventional PCB 100. The illustrated conventional PCB 100 has a structural core 102. This structural core 102 provides a rigid support to which other parts of the PCB 100 may be applied or electronic devices may be attached. The structural core 102 in this case has four core structural layers 104, 106, 108, 110. These core structural layers 104, 106, 108, 110 are each a fiberglass/resin composite material. The core structural layers 104, 106, 108, 110 have been pressed together and cured to form the structural core 102.
Above the top core structural layer 104 is a first top layer of conductive traces 112. These conductive traces 112 provide electronic connections to electronic devices that will be attached to the PCB 100. The conductive traces 112 may provide power or ground, or may allow electronic devices to communicate through use of electronic signals conducted by the traces 112. The first layer of conductive traces 112 is covered by a structural layer 114. This structural layer 114 is applied on top of the first layer of conductive traces 112 and cured. This process allows the structural layer 114 to fill in gaps between the traces 112 and adhere to the top layer 104 of the core 102 as well as to the traces 112 themselves. On top of the structural layer 114 is a second top layer of conductive traces 116. These traces 116 may also provide power or ground, or may allow electronic devices to communicate. The structural layer 114 separates the first and second top layers of conductive traces 112, 116, and insulates the traces 112, 116 from each other.
Similarly, below the bottom core structural layer 110 is a first bottom layer of conductive traces 118, a structural layer 120, and a second bottom layer of conductive traces 122. Like the top layers of conductive traces 112, 116, the bottom layers of conductive traces 118, 120 may provide power or ground, or may allow electronic devices to communicate. The structural layer 120 separates the first and second bottom layers of conductive traces 118, 120, and insulates the traces 118, 120 from each other.
As modern electronic devices increase in complexity, speed, and capabilities, their requirements for communication capacity also has risen. Such modern devices may require more communication capacity than can be provided by even PCBs 100 with multiple layers of conductive traces 112, 116, 118, 120, such as the PCB 100 shown in FIG. 1.